The present invention relates generally to electrical filters, and more particularly, to a multiple passband filter that passes multiple frequency bands using the same propagating mode while rejecting unwanted bands.
The assignee of the present invention manufactures and deploys communication satellites that provide global communication services. Waveguide filters are employed in communication systems carried by such communication satellites.
Heretofore, certain combinations of filters have been employed to perform the same function as the present filter. One prior art design includes a dual manifold multiplexer bandpass filter combined with band reject filters. Another prior art design includes a dual passband filter using multiple waveguide modes. Thus, prior art filters have always had a single passband or a multiple passband with multiple waveguide modes.
However, no prior art filter has provided a multiple passband filter that passes multiple frequency bands using the same propagating mode while rejecting unwanted bands. It is therefore an objective of the present invention to provide for a multiple passband filter that improves upon prior art filter designs.
To accomplish the above and other objectives, the present invention is an improved filter that produces a multiple passband response in a single device. The multiple passband filter comprises a plurality of poles concentrated in a desired passband of the filter. A plurality of zeroes are located outside of the desired passband to form passband edges. One or more zeroes are located in a central portion of the passband to form multiple passbands within the passband edges.
An exemplary embodiment of the multiple passband filter includes a plurality of cavities, one of which comprises an input port and another of which comprises an output port. Each of the cavities comprises first tuning apparatus disposed along a first axis for tuning the cavity to resonance in a first resonant mode, second tuning apparatus disposed along a second axis that is substantially orthogonal to the first axis for tuning the cavity to resonance in a second resonant mode, and mode coupling apparatus for adjusting the amount of energy coupled between the first and second resonant modes, wherein the mode coupling apparatus of adjacent cavities is disposed orthogonal with respect to each other.
Each of the orthogonal resonant modes is independently tunable to realize a separate pole of a filter function. A plurality of poles are concentrated in a desired passband of the filter, a plurality of zeroes are located outside of the desired passband to form passband edges, and one or more zeroes are located in a central portion of the passband to form multiple passbands within the passband edges.
The present invention provides for an improvement over prior art filters having a single passband or prior art filters having a multiple passband with multiple waveguide modes. The present invention provides the simplest filter design that produces a waveguide filter having multiple (two or more) passband response. Other prior art filters use extra parts such as manifolds or circulators.